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You might want to look into 3M prestige window film for the windows directly affecting the tsat. I had some installed recently in a customers house and its amazing what that stuff can accomplish. You may need to have a contractor add balancing dampers to your branch lines and balance the flow accordingly to each room.

Northwest Arkansas via Chicago Area via Straight Up from There on Lake Superior

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Thank you for more ideas. As it turns out the tsat room is 3-4 degrees above most other rooms due to the sun load. I have heard of the 3M window film. A couple of things raise concerns about that solution: 1) The windows were installed in 1994 and are not new. 2) There are windows all along 70' of exterior wall making for quite a bit of window although most of the load is from the tsat room. 3) It is my understanding that this film is quite expensive with pro installation, well above $1,000.

Just read the installation manual for the Honeywell indoor sensor I mentioned previously. The tsat is very high quality and has the ability to hold the temp setting exactly. From the specs on the sensor I noticed that:

Sensor Accuracy in Degrees:
+/-1.5 F at 70 F (+/-.84 at 21 C)

An accuracy of +/- 1.5 degrees F doesn't seem to give the same accuracy as the tsat itself. Am I looking at this wrong or are there other sensors that are more accurate?

PS: Occurred to me that I may be talking apples and oranges here. Indeed the sensors may not be that accurate in detecting the true temp and indeed multiple locations might average out to a confusing result but the tsat itself should still hold very accurately to the perceived reading. Right?

PS: Occurred to me that I may be talking apples and oranges here. Indeed the sensors may not be that accurate in detecting the true temp and indeed multiple locations might average out to a confusing result but the tsat itself should still hold very accurately to the perceived reading. Right?

Thank you for more ideas. As it turns out the tsat room is 3-4 degrees above most other rooms due to the sun load. I have heard of the 3M window film. A couple of things raise concerns about that solution: 1) The windows were installed in 1994 and are not new. 2) There are windows all along 70' of exterior wall making for quite a bit of window although most of the load is from the tsat room. 3) It is my understanding that this film is quite expensive with pro installation, well above $1,000.

Just read the installation manual for the Honeywell indoor sensor I mentioned previously. The tsat is very high quality and has the ability to hold the temp setting exactly. From the specs on the sensor I noticed that:

Sensor Accuracy in Degrees:
+/-1.5 F at 70 F (+/-.84 at 21 C)

An accuracy of +/- 1.5 degrees F doesn't seem to give the same accuracy as the tsat itself. Am I looking at this wrong or are there other sensors that are more accurate?

PS: Occurred to me that I may be talking apples and oranges here. Indeed the sensors may not be that accurate in detecting the true temp and indeed multiple locations might average out to a confusing result but the tsat itself should still hold very accurately to the perceived reading. Right?

Something else to consider: When there is air MOVEMENT close to a temp sensor... the reading tends to be more accurate.

The rule of thumb (given we do not follow rules of thumb in this industry) is to mount the T-stat close to a return so air flows by the T-stat, not on an outside wall or a wall with ductwork inside it, and not the direct rays of the sun or any heat producing appliance (like a fireplace or kitchen stuff). All of these tend to affect/effect the temp sensing.

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Originally Posted by beenthere

...

If you only have 3 rooms that you want to average. There is an undocumented way to only use 3 remote sensors. If your installer has a problem figuring it out. Let us know.

My original HVAC guy is gone and I am working with the Bryant dealer that installed the original system in the house. The original system was a basic Bryant NG furnace/AC, not like the top-end York dual fuel HP we have now. He has agreed to install the sensors for a reasonable per hour rate but he is neither a York nor Honeywell tsat expert (but even to me a non-expert the tsat manual seems to be fairly clear).

I am getting ready to order the 2 indoor remote sensors that he and I agreed to, but I thought that I should read the tsat and remote indoor sensor manuals. I am NOT an expert on this stuff and the following quote from the manual raised a concern about the 2 sensor install:

MULTIPLE REMOTE INDOOR SENSORS INSTALLED (OPTIONAL)
If more than one remote indoor sensor is used, based on configuration during installer setup, either of the following options are available:

• The thermostat will display the temperature measured at the sensor locations (internal thermostat sensor is disabled). Sensors must be in square numbers (e.g., 4, 9, 16, and so on) and the displayed temperature will be an average of the temperatures measured at each location.
• The thermostat will display a 50-50 average of the temperature measured at the thermostat location and the average of the temperatures measured at the remote indoor sensor locations. In this case, the thermostat sensor still carries a 50% weighting of the displayed temperature.

I want to (need to, really) disable the tsat temp reading and rely on the average of the remote sensors, thus the first option seems right. However the statement about "Sensors must be in square numbers" seems to defeat our choice of 2 sensors. Does you quote above about a "undocumented" 3 sensor install have a baring on the number of sensors needed? Are you saying that I need to get at least 3 sensors and this is the only choice of more than 1 sensor and less than 4 sensors (2 squared) that we can make? Are there any downsides to a 3 sensor install? Is there a diagram or description of the undocumented 3 sensor install that my new HVAC guy will understand using the 3 sensor solution?

My original HVAC guy is gone and I am working with the Bryant dealer that installed the original system in the house. The original system was a basic Bryant NG furnace/AC, not like the top-end York dual fuel HP we have now. He has agreed to install the sensors for a reasonable per hour rate but he is neither a York nor Honeywell tsat expert (but even to me a non-expert the tsat manual seems to be fairly clear).

I am getting ready to order the 2 indoor remote sensors that he and I agreed to, but I thought that I should read the tsat and remote indoor sensor manuals. I am NOT an expert on this stuff and the following quote from the manual raised a concern about the 2 sensor install:

MULTIPLE REMOTE INDOOR SENSORS INSTALLED (OPTIONAL)
If more than one remote indoor sensor is used, based on configuration during installer setup, either of the following options are available:

• The thermostat will display the temperature measured at the sensor locations (internal thermostat sensor is disabled). Sensors must be in square numbers (e.g., 4, 9, 16, and so on) and the displayed temperature will be an average of the temperatures measured at each location.
• The thermostat will display a 50-50 average of the temperature measured at the thermostat location and the average of the temperatures measured at the remote indoor sensor locations. In this case, the thermostat sensor still carries a 50% weighting of the displayed temperature.

I want to (need to, really) disable the tsat temp reading and rely on the average of the remote sensors, thus the first option seems right. However the statement about "Sensors must be in square numbers" seems to defeat our choice of 2 sensors. Does you quote above about a "undocumented" 3 sensor install have a baring on the number of sensors needed? Are you saying that I need to get at least 3 sensors and this is the only choice of more than 1 sensor and less than 4 sensors (2 squared) that we can make? Are there any downsides to a 3 sensor install? Is there a diagram or description of the undocumented 3 sensor install that my new HVAC guy will understand using the 3 sensor solution?

Thank you so much for your help here, Beenthere.

There is a way to use 2 sensors. instead of getting 4 10,000 ohm sensors. You get 2 20,000 ohm sensors.

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Beenthere, I have no idea what you are saying in the statement: "There is a way to use 2 sensors. instead of getting 4 10,000 ohm sensors. You get 2 20,000 ohm sensors." I see that the total resistance is the same, 40,000 ohm, but all I was going to do was order for the HVAC pro the correct number of indoor sensors that my tsat manual says and these are:

- TSAT: YTH9421C1002/U

- INDOOR SENSOR: C7189U1005

I have no idea or documentation as to the resistance of the actual indoor sensor in the C7189U1005 unit and there are no options for different resistance levels on the item being ordered. HELP!

Those are 10,000 ohm sensors, and you would need a min of 4 of them to use them.

I said its undocumented. So you won't find anything about using 20,000 ohm sensors. And while there is no way to change the type of sensors with that stat, it doesn't matter. As long as we end up with 10,000 ohms at 77 degrees and are using NTC resisters.

The old number for the 20,000 ohm sensors is TR77701006, the new number is ahhh, I'm not sure anymore. I think TR21. 2 of them will give the 10,000 ohms at 77 degrees that thermostat needs.

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Originally Posted by beenthere

Those are 10,000 ohm sensors, and you would need a min of 4 of them to use them.

I said its undocumented. So you won't find anything about using 20,000 ohm sensors. And while there is no way to change the type of sensors with that stat, it doesn't matter. As long as we end up with 10,000 ohms at 77 degrees and are using NTC resisters.

The old number for the 20,000 ohm sensors is TR77701006, the new number is ahhh, I'm not sure anymore. I think TR21. 2 of them will give the 10,000 ohms at 77 degrees that thermostat needs.

Beenthere, I have been trying to get my HVAC pro, a Bryant guy all the way even down to the tsat, to research this before I order the indoor sensors but he won't put in any advanced effort. This is going to be an hourly rate install. He seems to think that the install instructions that come with the purchased indoor sensor C7189U1005 will tell him how to install 2 sensors when the manual says that you must install 1, 4, 9, etc. He also thinks that installing too many sensors would be useless since the averaging would defeat keeping any of the sensed rooms at the right temp. He likes the 2 sensor install scenario though.

I even contacted the tech support on Honeywell's web site but of course they say that it can't be done and to have the pro contact them. Here is Honeywell's response to my proposed two sensors install scenario:

"We realize that you desire to purchase no more than the necessary number of sensors. However, hard wired sensors like the C7189U must be installed in squared numbers for the thermostat to properly sense the appropriate resistance. There is no way to utilize resistors to accomplish this. (My emphasis)

I have determined that the "resisters" that you mention are really thermistors or temperature varying resistors. Unless I can tell him the exact model and how to wire them, I don't think that he is going to get this done (right) for me. Is there some way he could look this up or call somebody when he shows up for the install?

TR77701006 is the old model number of the sensors you need to only use 2 sensors. TR21 is the new model number for Honeywell.

Honeywell tech support won't tell you anything that is not in the install manual. And the install manual for the IAQ does not document using 20,000 thermistors. So they will tell you it can't be done. Their tech support often just reads form a book.

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Beenthere, this is hurting my brain, but I think that I may have an alternative solution using 2 "sensor" locations. It also stays within the 1, 4 , 9, etc. indoor sensors that Honeywell requires.

One of the options on configuring the Honeywell YTH9421C1002/U tsat using setting 340 is to use one real C7189U1005 indoor sensor and the original tsat. From the tsat manual "The thermostat will display a 50-50 average of the temperature measured at the thermostat location and the remote indoor sensor location". The downside to this is my HVAC pro will have to physically move the the tsat to a new more appropriate sensing location. He will then install one new indoor sensor at the other desired location.

- Does this sound like a valid solution using just the original tsat and one new indoor sensor that fits Honeywell's restrictions?

- What size plain physical plate will look good and cover the original tsat location hole in the (off-white) wall?

Beenthere, I appreciate your patience as this HVAC idiot works through a solution to a bad uneven house temperature problem.